Planet Venus is putting on a show for skywatchers by moving across the face of the Sun as viewed from Earth. The transit is a very rare astronomical event that will not be seen again for another 105 years.

Observers in north and central America, and the northern-most parts of South America saw the transit begin just before local sunset. The far northwest of America, the Arctic, the western Pacific, and east Asia will witness the entire passage. The UK and Europe, the Middle East, and eastern African must wait for local sunrise to see the closing stages of the transit.

Venus appears as a small black dot moving slowly but surely across the solar disc. Many citizens keen to get a view of the transit themselves have been attending special events at universities and observatories where equipment for safe viewing has been set up. For others, internet streams have provided an easy way to follow Venus’s slow trek. Scientists have been observing the transit to test ideas that will help them probe Earth-like planets elsewhere in the galaxy, and to learn more about Venus itself and its complex atmosphere.

Venus transits occur four times in approximately 243 years; more precisely, they appear in pairs of events separated by about eight years and these pairs are separated by about 105 or 121 years. The reason for the long intervals lies in the fact that the orbits of Venus and Earth do not lie in the same plane and a transit can only occur if both planets and the Sun are situated exactly on one line.

This has happened only seven times in the telescopic age: in 1631, 1639, 1761, 1769, 1874, 1882 and 2004. Once the latest transit has passed, the next pair will not occur until 2117 and 2125.

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An international team of astronomers discovered a rectangular‑shaped galaxy within a group of 250 galaxies some 70 million light years away.

Alister Graham from Swinburne University of Technology said the rare rectangular-shaped galaxy was a very unusual object. “It’s one of those things that just makes you smile because it shouldn’t exist, or rather you don’t expect it to exist. It’s a little like the precarious Leaning Tower of Pisa or the discovery of some exotic new species which at first glance appears to defy the laws of nature.”

The unusually shaped galaxy was detected in a wide field-of-view image taken with the Japanese Subaru Telescope for an unrelated program by Swinburne astrophysicist Dr Lee Spitler.The astronomers suspect it is unlikely that this galaxy is shaped like a cube. Instead, they believe that it may resemble an inflated disc seen side on, like a short cylinder.

Support for this scenario comes from observations with the giant Keck Telescope in Hawaii, which revealed a rapidly spinning, thin disc with a side‑on orientation lurking at the centre of the galaxy.

Despite its apparent uniqueness, partly due to its chance orientation, the astronomers have managed to glean useful information for modelling other galaxies. While the outer boxy shape is somewhat reminiscent of galaxy merger simulations which don’t involve the production of new stars, the disc-like structure is comparable with merger simulations involving star formation. The results will be published in The Astrophysical Journal.